Increasing recognition of the potential importance of diet in the etiology of cancer and heart disease has highlighted the need for methods to measure individual dietary intake that are sufficiently simple to be used in large epidemiologic studies and whose reproducibility and validity have been quantified. We propose to design and validate a food frequency questionnaire for a Mexican population that is capable of ranking individuals by relative intake of foods and nutrients (calories, total fat, protein, cholesterol, vitamin A, etc.). Such a questionnaire has never been developed specifically for the Mexican population. The proposed questionnaire will be based on previously collected data from a dietary survey in Mexico. A pre-test will be used to identify the foods which best discrimate between individuals for intake of various nutrients. For the validation phase, we will select a random sample of 200 women aged 30 to 55 years from a middle- to low-income area of Mexico city. Each women will complete the food frequency questionnaire and then collect four 4-day weighed diet records over a one-year period. The food frequency questionnaire will be administered again at the end of the year and a blood specimen will be collected at that time. The blood will be analyzed for beta-carotene, alpha-tocopherol, retinol, and lipids. The reproducibility (initial versus repeated questionnaire) and validity (questionnaire versus diet records and blood parameters) will be evaluated using correlation and contingency table analyses. A validated method to assess dietary intake will permit the evaluation of etiologic hypotheses relating diet with cancer and coronary heart disease, which are increasing problems in Mexico. Future epidemiologic findings obtained from this population which has a wide variation in dietary intake will provide unique information about the effect of low intake of animal fat and vitamin A that cannot be explored in most developed countries and would be relevant for the large Hispanic population living in the U.S.